It often happens that several hydraulic or pneumatic rams should have synchronized movements, i.e., that their positions should be the same or should be staggered by the same value at any instant. This is particularly the case with rams which move the cylinders of machines for bending sheet metal.
To achieve very accurate synchronization, it has been found inadequate to control the rams identically, for example by coupling them in parallel or by connecting them by bars which, although rigid, undergo twisting in operation. It is necessary to provide a control system provided with a regulator capable of comparing the positions of the rams at any instant.